Investigating the impact of fecal contamination on antibiotic resistance genes in urban environments using host-associated molecular indicators

Antibiotic resistome of gut microbiota can be transmitted into the urban ecosystems via fecal pollution, potentially leading to a public health crisis. It is essential to determine the primary sources of fecal contamination and accurately evaluate the health risks for the propagation of antibiotic resistance genes (ARGs) from the intestinal microbiota. In this research, the occurrence, sources and potential hosts of ARGs in urban environmental samples collected from a wastewater treatment plant (WWTP), natural water bodies, tap water and farmland soil were comprehensively investigated. Host-associated fecal indicators for general warm-blooded animals (BacGeneral), humans (crAssphage), and other animals (bovines and swine) were employed for reliable microbial source tracking (MST). Results showed that the fecal indicator BacGeneral was detected in 84.00 % of collected environmental samples, indicating the widespread fecal contamination in local water and farmland. The WWTP was the reservoir and main source of fecal contamination in local environment, harboring the highest total abundances of ARGs (3.85 ± 2.72 ARGs/16S rRNA) and mobile genetic elements (MGEs) (0.32 ± 0.12 MGEs/16S rRNA) from multiple animals and humans. Although the swine-associated indicator was undetected, fecal contamination from both bovines and humans was prevalent in collected samples, with detection rates of pollution indicators at 52.00 % for bovine and 28.00 % for human sources. The co-occurrence of ARGs, fecal indicators and MGEs was analyzed, and significant correlation (P < 0.01) between total ARG abundance and fecal indicator (BacGeneral) in contaminated environments demonstrated that fecal pollution exhibited a great influence on overall resistome in local environment. This research offers a comprehensive understanding of the sources and dissemination of ARGs in feces-polluted urban environments, providing data for the monitoring and prevention of ARG pollution.